1. Field of the Invention
The present invention relates to a character display apparatus, a character display method, and a character display program capable of displaying a character with a high quality using a color display device, and a recording medium for use with such apparatus, method, and program.
2. Description of the Related Art
Japanese Laid-Open Publication No. 2001-100725 describes a known, conventional technique of displaying a character using a color display device. According to this technique, the intensity of a color element (e.g., brightness level) of a sub-pixel corresponding to a basic portion of a character is set to a predetermined value, while the intensity of a color element of a sub-pixel located adjacent to the sub-pixel corresponding to the basic portion of the character is set to a value different from the predetermined value. The number of sub-pixels whose color element intensities are set to values different from the predetermined value, and the color element intensities of these sub-pixels, are determined based on a correction pattern.
FIG. 43 shows an example where the intensities of sub-pixels corresponding to a basic portion of a character “/ (slash)” is set to a predetermined value according to the conventional technique described in Japanese Laid-Open Publication No. 2001-100725. In FIG. 43, each hatched box represents a sub-pixel corresponding to the basic portion of the character “/”. Where the color element intensity of a sub-pixel is represented by brightness levels 0–255, the color element intensity of a sub-pixel corresponding to the basic portion of the character “/” is set to, for example, “brightness level 0” (predetermined value). In FIG. 43, each open box represents a sub-pixel corresponding to the background of the character “/”. The color element intensity of a sub-pixel corresponding to the background of the character “/” is set to brightness level 255, for example.
FIG. 44 shows an example where the color element intensities of sub-pixels located adjacent to sub-pixels corresponding to the basic portion of the character “/” are set to values different from the predetermined value according to the above conventional technique. In the example illustrated in FIG. 44, the color element intensities of three sub-pixels located adjacent to each of the left and right sides of a certain sub-pixel which corresponds to the basic portion of the character “/” are set, based on a preset correction pattern, to “brightness level 73”, “brightness level 182” and “brightness level 219” in this order from the sub-pixel closest to the basic portion of the character to the farthest one from the basic portion of the character. Hereinafter, in this specification, setting the color element intensity of a sub-pixel located adjacent to a certain sub-pixel corresponding to a basic portion of a character based on a correction pattern is referred to as “placing a correction pattern”.
The reasons why a correction pattern is placed are to suppress color noise in a character (i.e., to make the character look black to a human eye), and to adjust the width of lines included in the character to a desired width.
Thus, according to the conventional technique, a correction pattern is placed adjacent to a sub-pixel corresponding to a basic portion of a character, whereby the character is displayed with a high quality.
A basic portion of a character is included in a frame having a certain size. A sub-pixel corresponding to the basic portion of the character is included within a region on a display plane of a display device which corresponds to the frame.
FIG. 45 shows a relationship between sub-pixels corresponding to a basic portion of a character “A” and a region corresponding to a frame. In FIG. 45, each hatched box represents a sub-pixel corresponding to the basic portion of the character “A”. A region 1021 represents a region on a display plane which corresponds to a frame of the character “A”.
FIG. 46 shows an example where the color element intensities of sub-pixels located adjacent to sub-pixels corresponding to the basic portion of the character “A” are set to values different from the predetermined value according to the above conventional technique. In the example illustrated in FIG. 46, three adjoining sub-pixels have to be secured for placing a correction pattern. However, within the region 1021 corresponding to the frame of the character “A”, there are only two sub-pixels (sub-pixels 1034 and 1035) located adjacent to the right side of a sub-pixel 1031. Similarly, within the region 1021, there is only one sub-pixel (sub-pixel 1036) located adjacent to the right side of a sub-pixel 1032. Therefore, a correction pattern cannot be placed at the right sides of the sub-pixels 1031 and 1032 so as to all fit within the region 1021.
Conventionally, a character is displayed on a display device such that the character is placed within a region on a display plane of the display device which corresponds to a frame of the character. If a correction pattern at a portion of the region 1021 (i.e., portion 1033) cannot be placed entirely within the region 1021, as shown in FIG. 46, color noise occurs in such a portion and therearound, and/or the width of a line of the character at that portion cannot be seen as having a desired width. As a result, the character cannot be displayed on the display device with a high quality.
FIG. 47 shows an example where the color element intensities of sub-pixels located adjacent to sub-pixels corresponding to a basic portion of a character “H” are set to values different from the predetermined value according to the above conventional technique. In the example illustrated in FIG. 47, in a portion of the right vertical line of the character “H” (portion 1041), a correction pattern cannot be placed within the region 1021 which corresponds to a frame of the character “H”. As a result, color noise occurs in the portion 1041, and the width of a line of the character at the portion 1041 cannot be seen as having a desired width. In this example, the right vertical line of the character “H” looks thinner than the left vertical line of the character “H”. As a result, the character “H” cannot be displayed on the display device with a high quality.